Cost per conversion (CPA)

Cost per conversion — CPA, cost per acquisition — is the total spent divided by the number of conversions it produced. It is the one number that lets two campaigns, two keywords or two channels be compared on the same axis, provided both are counting the same kind of result. It also sets the bar for waste: a keyword that has spent three times the account's normal cost per conversion with none to show for it is not unlucky, it is a leak. A channel with no tracked conversions has no CPA at all — its cost is effectively infinite, never cheap — which is why a verdict between Google and Meta cannot be made until both sides are counting.